Drift near Seattle, Taeoiiia and Ohnnpia. — Cphani. 21 t 
thick, is overlain by 5 or 8 feet of tlie ordinary coarse yellow 
gravel. 
Although there is little or no till at and near the drift, 
border south of Puget sound, and although that belt has no 
large drift accumulations, the thin edge of the modified drift 
presents distinct but very low mounds and knolls, ridges and 
hollows, more or less referable to the class of marginal kames, 
which in many drift regions are a conspicuous feature of ter- 
minal and recessional moraines. Frequently only 2 to 5 feet 
high, but occurring in great profusion, by hundreds and even 
thousands, without any evident system or order of grouping, 
these peculiar gravel mounds, characterizing especially the 
open tracts of prairie in this mainly wooded district, are one 
of the most remarkable phases of terminal drift deposition. 
They seem to me correlative with the commonly hilly terminal 
moraine belts of other drift areas. 
A good description of these mounds, and discussion of their 
mode of formation, have been given by ]\Ir. G. O. Rogers,* 
with illustrations of the probable conditions of the melting ice 
margin from Russell's observations of the present glaciers of 
Alaska. Other suggestions to account for the origin of the 
mounds, as by Prof, Joseph Le Conte.t Avho ascribed them to 
erosion of a formerly smooth deposit, are shown by Rogers 
to be inapplicable. 
Passing southward from Olympia by either of the two rail- 
ways, one sees the mounds of this marginal drift belt in 
countless numbers. The following details of the prairie areas 
which they occupy there and eastward were not supplied by 
Rogers nor Le Conte, excepting their general statements that 
the "mound prairies" are. as Rogers wrote, "a few miles south 
of Olympia." being, as Le Conte wrote, "at the southern ex- 
tremity of Puget sound." 
About ten miles south from Olympia. and three to five 
miles north of Tenino, they have given name to Rocky prairie, 
because of the exceedingly abundant waterworn cobbles of the 
gravel which forms the general prairie and also the mounds. 
This prairie is crossed centrally by the railway for two miles. 
• "Drifts Mounds near Olympia, Washington," Amer. Geologist, vol. xi. 
pp. 393-399, Tune, 1893. 
t Proceedings of the California Academy of Sciences, Dec. 15, 1873. 
